In order to extract the required messages.db from the WhatsApp backup:

  1. open File Explorer app on your Lumia
  2. click the backup taken with App Data Manage Tool (data)
  3. access 5319275A.WhatsApp_cv1g1gvanyjgm\LocalState\messages.db
  4. share the messages.db in any way you want (One Drive/Google Drive/email/bluetooth) so that you can transfer it to your Android phone